The present invention relates to a metal gasket for an internal combustion engine, which includes double beads, i.e. inner bead and outer corrugated bead, to securely and widely seal around a hole.
An engine and a gasket installed therein for an automobile include cylinder bores, water holes, oil holes, bolt holes and so on. Since high pressure and temperature are formed in the cylinder bores when the engine is actuated, bolts for securing the engine parts together with the gasket are generally arranged around the cylinder bores to securely seal therearound. Other holes, such as water holes and oil holes, are situated near the cylinder bores, and are sealed by the tightening pressure of the bolts for sealing the cylinder bores.
Therefore, the other holes, i.e. water holes and oil holes, do not generally receive equal tightening pressure from the bolts. As a result, although the other holes have sealing means in the gasket, various sealing problems occur in these other holes.
For example, in case a rigidity of a cylinder head and/or cylinder block is not strong, no matter where a hole to be sealed is located, i.e. even if the hole is located away from or close to the bolt holes, the sealing means of the gasket may not be sufficiently compressed to possibly cause leakage. On the other hand, in case the rigidity of the cylinder head and/or cylinder block is strong, if sealing means for a hole is not strong against a high tightening pressure, the sealing means is weakened or creeps by the high tightening pressure to thereby cause leakage as well. Regardless of the rigidity of the engine, if the sealing means is formed close to the cylinder bore, the sealing means may creep by high temperature to possibly cause leakage.
Further, in an elongated engine, since the sealing means are formed around the cylinder bores of the gasket, when the engine is assembled, the center area of the cylinder head is liable to bent upwardly while the longitudinal end areas are compressed close to the cylinder block. Therefore, high tightening pressures are concentrated at the longitudinal end areas of the gasket.
In order to solve the problems, various attempts have been made. For example, a bead for surrounding a fluid hole is partially doubled at a portion away from the bolt hole to increase the surface pressure at the doubled portion, and a strength of a bead surrounding a fluid hole is partially changed to regulate the surface pressure. Also, in U.S. Pat. No. 5,570,892, a portion of a bead away from bolt holes where a high surface pressure is not formed is corrugated to form a wide corrugated bead portion. Further, in U.S. Pat. No. 5,439,234, beads around the cylinder bores located at the longitudinal end portions are doubled to support the strong tightening pressures applied thereto.
In Japanese Utility Model Publication (KOKOKU) No. 8-5419, an expandable corrugated bead is formed around a circular bead outside a cylinder bore, wherein the corrugated bead receives tightening pressure less than that on the other portions.
The conventional sealing means or beads around the fluid hole can seal properly as intended. However, the sealing can not be always made properly by the conventional sealing means or beads because of the difference of the surface pressure applied to the sealing means.
The present invention has been made in view of the conventional gaskets, and an object of the invention is to provide a metal gasket for an internal combustion engine, which can securely seal around a hole by double beads.
Another object of the invention is to provide a metal gasket as stated above, which can provide a wide sealing area to withstand high pressure applied thereto.
A further object of the invention is to provide a metal gasket as stated above, wherein the wide sealing area can be formed as desired.
Further objects and advantages of the invention will be apparent from the following description of the invention.